For problem statement at 0-999/900-999/960-969/962/problemG.txt this is a correct solution, but verifier at 0-999/900-999/960-969/962/verifierG.go ends with case 20 failed: expected 0
 got 1
input:
17 16 18 11
4
17 16
19 16
19 12
17 12
exit status 1 can you fix the verifier? ```go
package main

import (
	"bufio"
	"fmt"
	"io"
	"math/bits"
	"os"
)

type FastScanner struct {
	data []byte
	idx  int
}

func NewFastScanner() *FastScanner {
	data, _ := io.ReadAll(os.Stdin)
	return &FastScanner{data: data}
}

func (fs *FastScanner) NextInt() int {
	n := len(fs.data)
	for fs.idx < n {
		c := fs.data[fs.idx]
		if c == '-' || (c >= '0' && c <= '9') {
			break
		}
		fs.idx++
	}
	sign := 1
	if fs.data[fs.idx] == '-' {
		sign = -1
		fs.idx++
	}
	val := 0
	for fs.idx < n {
		c := fs.data[fs.idx]
		if c < '0' || c > '9' {
			break
		}
		val = val*10 + int(c-'0')
		fs.idx++
	}
	return sign * val
}

func main() {
	in := NewFastScanner()

	wx1 := in.NextInt()
	wy1 := in.NextInt()
	wx2 := in.NextInt()
	wy2 := in.NextInt()

	if wx1 >= wx2 || wy2 >= wy1 {
		out := bufio.NewWriterSize(os.Stdout, 1<<20)
		fmt.Fprint(out, 0)
		out.Flush()
		return
	}

	n := in.NextInt()
	events := make([][]int, 15002)

	fx := in.NextInt()
	fy := in.NextInt()
	px, py := fx, fy

	for i := 1; i < n; i++ {
		x := in.NextInt()
		y := in.NextInt()
		if x == px {
			a, b := py, y
			if a > b {
				a, b = b, a
			}
			events[a] = append(events[a], x)
			events[b] = append(events[b], x)
		}
		px, py = x, y
	}

	if px == fx {
		a, b := py, fy
		if a > b {
			a, b = b, a
		}
		events[a] = append(events[a], px)
		events[b] = append(events[b], px)
	}

	width := wx2 - wx1
	words := (width + 63) >> 6
	curr := make([]uint64, words)
	prev := make([]uint64, words)

	all := ^uint64(0)
	lastMask := all
	if rem := width & 63; rem != 0 {
		lastMask = (uint64(1) << uint(rem)) - 1
	}

	var aCount, bCount, cCount, dCount int64
	havePrev := false

	for y := 0; y < wy1; y++ {
		for _, x := range events[y] {
			if x >= wx2 {
				continue
			}
			if x <= wx1 {
				for i := 0; i < words; i++ {
					curr[i] ^= all
				}
			} else {
				start := x - wx1
				wi := start >> 6
				bi := uint(start & 63)
				curr[wi] ^= all << bi
				for i := wi + 1; i < words; i++ {
					curr[i] ^= all
				}
			}
		}

		curr[words-1] &= lastMask

		if y < wy2 {
			continue
		}

		var ones, hadj, vadj, blocks int64
		var carry1, carry2 uint64

		if havePrev {
			for i := 0; i < words; i++ {
				w := curr[i]
				ones += int64(bits.OnesCount64(w))
				hadj += int64(bits.OnesCount64(w & ((w << 1) | carry1)))
				carry1 = w >> 63

				c := w & prev[i]
				vadj += int64(bits.OnesCount64(c))
				blocks += int64(bits.OnesCount64(c & ((c << 1) | carry2)))
				carry2 = c >> 63
			}
			cCount += vadj
			dCount += blocks
		} else {
			for i := 0; i < words; i++ {
				w := curr[i]
				ones += int64(bits.OnesCount64(w))
				hadj += int64(bits.OnesCount64(w & ((w << 1) | carry1)))
				carry1 = w >> 63
			}
			havePrev = true
		}

		aCount += ones
		bCount += hadj
		copy(prev, curr)
	}

	ans := aCount - bCount - cCount + dCount

	out := bufio.NewWriterSize(os.Stdout, 1<<20)
	fmt.Fprint(out, ans)
	out.Flush()
}
```